Adaptive beamforming algorithms for wireless link layer multicasting

The proliferation of mobile applications and services involving group communications has increased the need for efficient wireless multicasting solutions in next generation broadband access networks. The availability of antenna arrays at the base stations makes adaptive beamforming especially attractive for multicasting; with beamforming, the received signal strength at the clients can be significantly improved. However, the problem of designing optimal transmit beamformers for multicast applications is challenging, mainly due to its non-convex nature. In this work, we design efficient transmit beamformers for wireless link layer multicasting where instantaneous channel state information is available at the transmitter. In addressing the non-convexity of the problem, we design non-iterative, near-optimal beamforming algorithms based on the optimality conditions derived from its Lagrangian formulation. We show that for real channels, e.g, where Pulse Amplitude Modulation (PAM) is used, the optimal solution can be obtained. To address the effectiveness of the proposed solution for the complex channel, we also derive an upper bound on the multicast rate based on the dual formulation of the problem. Evaluations reveal that our algorithms deliver a performance that is close to the upper bound, while significantly improving the multicast rate over state of the art solutions.